1. Field of the Invention
The present invention relates to a process for producing retort boiled rice directly from raw rice, with no coloring of rice.
2. Discussion of the Background
Heretofore, retort rice has been produced by a method in which raw rice is boiled at about ambient pressure, and a predetermined quantity of rice so boiled or steamed is weighed and charged into a container, followed by sealing and retorting. Alternatively, retort rice has been produced by charging a predetermined quantity of raw rice into a container together with water, sealing the container, and then performing the boiling and sterilization of the rice under retort conditions. In either method, however, the resulting boiled rice is inevitably colored brown.
If raw rice is charged into a container or bag together with water and, after the sealing of the container or bag, boiled under retort conditions without replacing, neither in part nor whole, the air in the head space of the container or bag with an inert gas, there is results boiled rice having a brown color. In the case where all of the air in the head space above the rice and water is replaced with an inert gas, such as nitrogen gas or the like, for the purpose of avoiding the undesirable coloring, there results boiled rice having a bluish light gray color. This undesirable coloring can be avoided if the boiling of the rice is carried out at a relatively low temperature for a prolonged period of time. In this method, however, a retort rice product having inferior preservability results due to insufficient sterilization. In addition, it is time-consuming and hence requires energy in quantities larger than in the present invention.
In view of the above problems, a need continues to exist for a process for producing retort boiled rice which is free from the undesirable coloring.
It is presumed that the coloring (browning) is caused by reaction products between oxygen and certain components of rice or products formed through decomposition of certain rice components. It is also presumed that the browning phenomenon is related to not only oxygen, but also heating temperature and time. The phenomenon does not take place at temperatures of ordinary home use pressure cookers. However, the surface of boiled rice becomes colored under high temperature retort conditions (120.degree. C. or above) commonly employed in the food industry, if oxygen is present in the system in quantities above a certain level.